1. Field of the Invention
The present invention relates to biological degradation of ferric chelates of aminopolycarboxylic acids. More particularly, the invention relates to the use of the microorganism Agrobacterium sp. to degrade these compounds, especially from aqueous solutions, as well as to biologically pure cultures of Agrobacterium sp.
2. State of the Art
It has heretofore been recognized that metal chelates of aminopolycarboxylic acids, such as ferricethylenediaminetetraacetic acid (ferric-EDTA) and other similar chelates, were not readily biodegraded. See, for example, Gerike et al., Ecotoxicology and Env. Safety, 3:159-173 (1975).
This inability to readily degrade such metal chelates leads to numerous environmental concerns. In particular, in secondary treatment with an activated sludge, the biodegradation of these metal chelates is so slow that these chelates have been reported to pass through secondary treatment facilities and discharged into the environment without notable degradation. See Thom et al., Proc. Roy. Soc. of London, 189:347-357 (1975). This has led to concerns for the possible bioaccumulation of the chelate in the environment as well as the possible transport of heavy metals by release of high concentrations into polluted rivers or sediments. Additionally, EDTA has also been implicated in the mobilization of radionuclides from nuclear waste disposal sites.
On the other hand, accumulation of EDTA in the environment over time periods on the order of years has been shown to be unlikely. For example, EDTA contamination in soil, at relatively low concentrations (2-1000 micrograms per gram of soil), have been demonstrated to be biologically removed. See Tiedje, Appl. Microbiol., 30:327-329 (1975) and Tiedje, J. Environ Qual. 6:21-26 (1977). In these studies, the disappearance of low concentrations of EDTA and its metal chelates was shown to occur in 15-45 weeks on a wide variety of soils. However, no single bacterial type was isolated which was capable of metabolizing EDTA or its metal chelates.
At somewhat higher concentrations (&lt;2 mM) in aqueous solution, Belly et al., Appl. Microbiol, 29:787-794 (1975) have investigated the aerobic bacterial degradation of the Fe.sup.+3 EDTA chelate by an acclimated mixed population of bacteria. Disappearance of more than 90% of the substrate in 5 days was observed at these concentrations. Again, no single bacterial type was isolated which would grow on the ferric-EDTA substrate as sole carbon source.
The abstract for SU 525627 describes removal of heavy metal complexes from water by precipitation, using first a sodium hydroxide treatment and then biological purification using aerobic microorganisms. The filtrate obtained from the sodium hydroxide treatment is purified with microorganisms at a pH of 8-9.
Japanese Laid-Open Patent Application (Kokai) No. 58-43782 states that strains of the genera Pseudomonas and Alcaligenes are capable of degrading EDTA under aerobic conditions. The maximum concentration tested was 5 mM and required 5 days for 80% degradation.
Besides biological degradation, the ferric chelate of EDTA can be degraded by ultraviolet irradiation. Specifically, under simulated environmental conditions, Lockhart et al., Env. Sci. and Technol., 9:1035-1038 (1975) as well as Lockhart et al., Environ. Lett., 9:19-31 (1975) have demonstrated degradation by the mechanism of UV irradiation. Rates of degradation in bright sunlight were found to vary from 1-2 days for removal of the parent compound at an initial concentration and pH of 1.6 mM and 4.9, respectively, to greater than 10 days at an initial concentration and pH of 9.8 mM and 6.9, respectively. In these studies transformation of ferric-EDTA was demonstrated but extensive mineralization was not.
In view of the above, there is a continuing need in the art for an efficient method for the degradation of metal chelates of aminopolycarboxylic acids, especially from industrial waste solutions contaminated with such chelates. There is a further need in the art that any such degradation process for the removal of such chelates be conducted rapidly without damaging the environment.